addition of hydrogen to ni-ti multilayers:
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Addition of Hydrogen to Ni-Ti Multilayers:Implications for Neutron Monochromator and Supermirror Performance
Brent J. HeuserDept. Nuclear, Plasma, & Radiological Engineering
University of Illinois at Urbana-Champaign
Supported by the DOE INIE Program
OutlineIntroduction—neutron monochromators, supermirrors, & guidesSample preparation—magnetron sputtering (Ar or Ar+H2 gas)Experimental results—NR, XRD, AFM, AES, TPD analysisDiscussion—effect of H; correlation between NR, AFM, & AES
Acknowledgements
Hyunsu Ju (NPRE UIUC)Sungkyun Park (IPNS ANL)Rick Goyette (SNS ORNL)
UIUC FS-MRL staff:Tony BanksNancy FinneganScott MacLarenVania PetrovaMauro Sardela
Cold Neutron Guide Halls Orphée Reactor & Guide Hall at the LLB, Saclay
NIST Reactor & Guide Hall
Neutron guides transport long wavelengthneutrons far from reactor containmentwhere neutron and gamma-ray backgrounds are much lower.
Guides are based on total external reflectionand must be very efficient.
Cold SourceScattering Instrument
Neutron Guides
VacuumReflective coatings
Neutron GuidesEvacuated channels with coatings on top, bottom, and sides that reflect neutrons.
LH2 or CH4
~4-25 K
Review of Basic Neutron Optical Elements
R
c or Qc
1 2
c
Nb=
or Q
fixed
Single-layer films
InterdiffusionbarrierTi (Nb = -1.95 x 10-6 A-2)
Ni (Nb = 9.40 x 10-6 A-2)
Multilayer filmsR
Q
d
2Q
d
R
c
1 2
c= Nb
fixed
Bare Si Substrate
Substrate + Nickel Coating
Substrate + Ni-58 Coating
Substrate + Ni-Ti Multilayer Coating
Review of Basic Neutron Optical Elements
Total External Reflection
Qc
4QcCθ
guide
monochromator
Review of Basic Neutron Optical Elements
NiC-Ti
Hino et al., NIMB, 529 (2004) 54.
Supermirror films
R
Q
Continuous distribution of d-spacingvalues extends critical edge
=8.8Å
2
cI
Neutron guides Internal coatingNatural Ni
Ni-58 (Gain~1.5)Ni-Ti Supermirror (Gain~m2)
Must be able toaccept larger
angular divergenceor use shorter
wavelength neutrons
Fabrication of Ni-Ti Multilayer Films Using Magnetron Sputtering
Samples~500 Å Ni~500 Å Ti1 Ni-Ti BL2 Ni-Ti BL4 Ni-Ti BL6 Ni-Ti BL
10 Ni-Ti BL15 Ni-Ti BL20 Ni-Ti BL40 Ni-Ti BL
Growth rate: 0.4 Å /secBi-layer spacing: ~80 Å
Substrate @ RT
Sputter Gas2.7 mT Ar
2.7 mT Ar + 0.3 mT H2
Neutral sputtered atoms
Two separate targets:Ti or Ni
plasmamagnetic fieldlines
-V
Neutron Reflectivity Measurements—POSY 2 @ IPNS-ANL
40 BL 20 BL
6 BL
2 BL
10 BL
4 BL
R vs. Q—measurements and fits
w/o H
w/H
w/H
w/Hw/H
w/H
w/o H
w/o Hw/o H
w/o H w/o H
w/H
R vs. BL Number
Reflectivity Ratio
6 BL
6 BL
Fits to the Neutron Reflectivity Measurements
Fits not unique!
Atomic Force Microscopy Measurements of Surface Roughness
2 BL w/o H 4 BL w/o H 6 BL w/o H
40 BL w/o H20 BL w/o H10 BL w/o H
500 Å Ni 500 Å Ti 500 Å TiH2
Ra=1.4 Å Ra=1.6 Å Ra=1.8 Å
Ra=5 Å Ra=7 Å Ra=9 Å
Ra=15 ÅRa=4 Å Ra=11 Å
Gradual increase in roughness of top surface is observedthat is consistent withdegradation of reflectivityfor BL > 6.
Auger Electron Spectroscopy Measurements of Atomic Concentration
Oxygen content at noise level; oscillations in oxygen signal in 20 w/H ML sample have same period as Ti and Ni oscillations, but correlated to Ti.
Concentration profiles for Ti in the with-hydrogen ML samples are flat indicating uniform hydrogen concentration within Ti layers.
Ti and Ni signal oscillations in ML samples dampen away from the film-substrate inter-face, consistent with increase surface roughness for high BLnumber observed with AFM.
20 ML w/o H (old Ti target)
20 ML w/H
20 ML w/o H (new Ti target)
20 ML w/o H (old Ti target)
20 ML w/H
Correction to Theoretical 1st Order Peak Reflectivity
)exp(-Q 2rms
2calcreal RR
Temperature Programmed Desorption Measurements of Hydrogen Concentration
TiH2 powder500 A Ti
40 ML
2 ML
Concentration of hydrogenproportional to area under curve. Sample [H]/[Ti]
500 A 2.0
40 ML w/H 2.0
20 ML w/H 2.2
10 ML w/H 1.5
6 ML w/H 2.5
4 ML w/H 1.7
2 ML w/H 1.7
40 ML w/o H 0.7
20 ML w/o H 0.8
10 ML w/o H 1.0
6 ML w/o H 0.8
4 ML w/o H 0.9
2 ML w/o H 1.2
40 ML w/o H 0.4
20 ML w/o H 0.3
Conclusion
Addition of hydrogen to Ti works—increase in 1st order diffraction peakreflectivity observed. Gains in on-sample intensity of 2-3 should be possible without too much effort.
Degradation in 1st order peak reflectivity with BL value consistent withsurface roughening observed with AFM.
Larger interfacial roughness as BL value increases was observed with AES, consistent with AFM.
Munter et al., Physica B 221 (1996) 500.
Substitution of Be for Ni + Addition of H to Ti
Orphee Reactor—LLB Saclay
NBS Reactor LH2 Cold SourceNIST
Auger Electron Spectroscopy Measurements of Atomic Concentration
Oxygen content at noise level; oscillations in oxygen signal in 20 w/H ML sample have same period as Ti and Ni oscillations, but correlated to Ti.
Concentration profiles for Ti in the with-hydrogen ML samples are flat indicating uniform hydrogen concentration within Ti layers.
Ti and Ni signal oscillations in ML samples dampen away from the film-substrate inter-face, consistent with increase surface roughness for high BLnumber observed with AFM.
Bulk Ni
Bulk Ti
20 ML w/o H
20 ML w/H
40 ML w/H
10 ML w/H
Addition of Hydrogen to Ni-Ti Multilayers:Implications for Neutron Supermirror Performance
Brent J. Heuser, UIUCHyunsu Ju, UIUC
Sungkyun Park (ANL), Rick Goyette (ANL), Tony Banks (UIUC), Nancy Finnegan (UIUC), Scott MacLaren (UIUC), Vania Petrova (UIUC)
Mauro Sardela (UIUC)
Supported by the DOE INIE Program
1. Neutron optics—monochromators and supermirrors2. Sample preparation.3. Experimental results—NR, XRD, AFM, AES, TPD analysis
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